One is relative the other absolute...Motor.A.rotateTo(90); // Rotates by 90 degrees to the absolute 90 degree pointMotor.B.rotate(90); // Rotates 90 degrees from current location, so in this case will move to 90 degreesMotor.A.rotateTo(90); // Will not move as the motor is already at the absolute 90 degree pointMotor.B.rotate(90); // rotates by 90 degrees from current location, so at the end of the move the motor will be at 180 degrees

To understand this sort of thing the best way is simply to try it and see what happens....